A man who allegedly attacked an officer with a tree branch was killed in a police shooting in San Fernando Thursday. An investigation is under way.

Authorities say the shooting happened in the 800 block of Truman Street at 5:45 a.m. Detectives say a San Fernando police officer confronted an assault suspect, a man in his 50s or 60s, in the parking lot of a liquor store.

The man, who was described as a transient, allegedly began hitting the officer's patrol car with a blunt object. The officer used a Taser in an attempt to stop the suspect, but then the man began to attack the officer with the blunt object, police said.

"The suspect was armed with a tree branch, which is very sharp on one end and very thick on the other," said Lt. Mike Rosson of the L.A. County Sheriff's Department.

Rosson said the Taser was not effective, likely because of the layers of clothing the suspect was wearing.

The officer opened fire on the suspect. The man was taken to a local hospital with one gunshot wound to the upper torso. He was pronounced dead a short time later. His name has not been released.

The officer was not injured in the incident. He is on administrative leave as an investigation into the shooting begins. Anyone with information about the shooting is urged to call the L.A. County Sheriff's Department at (323) 890-5500.